The present invention relates to material handling apparatus and more particularly to an improved agricultural feed grinding and mixing machine.
Most present day agricultural fed grinding and mixing machines, commonly referred to as grinder-mixers, comprise a vertical mixing assembly mounted concentrically within a mixing tank having a cylindrical upper section and a frusto-conical shaped downwardly converging lower section. The mixing assembly includes a centrally located upright mixing auger rotatably mounted within a tubular housing and having inlet and discharge openings at its upper and lower ends, respectively. During a mixing operation, feed material is conveyed in a generally circuitous path. The mixing assembly continually transfers material from the bottom of the tank upwardly through the auger housing to the top of the tank whereupon it is discharged through the upper opening and allowed to gravitate back down toward the lower portion of the mixing tank. Commercially available apparatus of this type is illustrated by U.S. Pat. No. 3,780,993 issued Dec. 25, 1973, to Charles M. Kline, one of the joint inventors of the present invention.
The conical section of the mixing tank configuration of the grinder-mixer described above functions to direct material inwardly towards the central mixing auger as it settles or gravitates downwardly during circulation. Since the horizontal cross section of the tank decreases substantially as the walls converge inwardly, the material is compressed as it settles causing certain feed materials, especially those being processed under moist and/or extremely soggy conditions, to form a cluster of relatively dense material. This is illustrative of a common problem during operation of commercially available grinder-mixer machines having conventional conical shaped lower sections. Material moving downwardly in the tank tends to build up in the area between the lower walls of the tank and the auger housing. This buildup, commonly referred to as "bridging," restricts free downward flow of material and thereby impedes a smooth circuitous flow of material which in turn diminishes the overall machine effectiveness. Certain crop conditions lead to more frequent bridging and many times shutdown is necessary to permit manual removal of material from plugged areas.
One prior art arrangement that overcomes the problem of bridging in the lower tank is shown in U.S. Pat. No. 3,780,993, mentioned above. In this arrangement, the central mixing auger includes a lower section of flighting having relatively wide outside dimensions. This configuration is designed to more effectively advance material contained in the lower portion of the tank and thereby obviate the forming of clusters of material in the vicinity of the lower sidewalls of the mixing tank. Although this type of auger has been generally successful, the overall efficiency of the mixing apparatus drops off under conditions where the feed material being processed is wet and soggy. This patent also features a auger provided with a plurality of outwardly projecting extensions on its lower wide diameter flighting. As the central mixing auger is rotated, the outwardly projecting extensions engage and agitate surrounding material to break up clusters in the vicinity of the auger and permit material being mixed to gravitate more freely to the base of the tank. Consequently, the extensions further enhance overall circulation of feed material within the tank during a mixing operation. Although this feature improves mixing capability under adverse conditions, it tends to create turbulence during circulation of dry crop materials prevalent in some geographical regions.
Another prior art approach that has been proffered as a solution to the problem of bridging in the lower tank portion of grinder-mixers is disclosed in U.S. Pat. No. 3,667,734, to A. D. Skromme et al, issued June 6, 1972. In this patent, the walls of the grinder-mixer are vertical and the material that gravitates to the bottom of the mixing chamber during operation is engaged by the blade of a long sweep arm rotating with and extending outwardly from the auger shaft. The arm sweeps through a path parallel to and encompassing the entire bottom of the tank. A similar sweep arm is employed in the vertical mixing tank disclosed in U.S. Pat. No. 1,576,018, issued Mar. 9, 1926, to R. B. Wolf. Although the vertical walls in this type of apparatus eliminate the problems caused by convergence at the lower portion of the mixing chamber, an inherent shortcoming of this type of apparatus is the tendency of material to wedge under the sweep arm causing an upward force component with obvious deleterious effects. This problem is apparently not alleviated when a guide is used to restrain the outer end and, in fact, the problem would seem to be compounded due to the tendency toward bridging between the sidewall and any ledge-like surface extending therefrom. A further disadvantage experienced during use of vertical sidewall type configurations is the need for a head of pressure, without which the sweep arm has a tendency to merely slide under the material without changing its relative position in the tank, especially during partial load conditions. This disadvantage is even more prevalent at the end of an unloading operation, i.e., where the weight of the load affects the ability of the sweep arm to impart a radial force to urge material toward an unloading port. Thus, the sweep arm operates best under full load conditions but conversely, the effects of wedging increase proportionately with the load.
There exists still another prior art approach to the problem of bridging in grinder-mixers having a conventional inverted conical-shaped lower tank portion inclined inwardly toward the central mixing auger assembly. For example, apparatus is sold by the Koehring Farm Division of Des Moines, Iowa, wherein the mixing assembly comprises an upper auger portion rotatable with a lower auger portion having an inverse frusto-conical shaped core section. In this arrangement the inclined wall commences at the approximate center of the tank and the bottom of the tank is completely covered by the lower core section, as shown and described in Koehring brochure No. 150472 NWC. A similar configuration is disclosed in U.S. Pat. No. 3,589,684, issued on June 29, 1971, to Bernard Dixon. The Dixon patent also shows a mixing tank with a vertical mixing assembly having a frusto-conical shaped lower core section covering the entire bottom and on a common shaft with an upper cylindrical auger. Both the upper and lower auger sections are concentrically journalled in the tank for rotation within a housing that is flared at the bottom in a shape adapted to accommodate the lower conical portion of the auger. In Koehring the auger tube does not include a flared portion at the lower end thereof, and thereby exposes the conical portion of the auger directly to the material sliding downwardly along the inclined tank wall.
In the Dixon arrangement, even though the flared enclosure has slotted apertures the conical portion of the housing would tend to cause bridging between it and the tank wall due to the convergence of material with no means to rapidly take it away. Bridging problems are exceptionally acute under conditions where crop material is damp as is the case in many areas of the world where grinder-mixers are employed. In the Koehring arrangement without a flared housing portion, even though material is allowed to contact the conical auger prior to reaching the bottom part of the tank, bridging problems due to the diminishing area between the auger housing and downwardly inclined tank wall are still of concern.